In a conventional gas-fired water heater, the gas burner is located beneath the lower head of the tank and waste gases of combustion are discharged from the burner through one or more vertical flues that extend upwardly through the tank. When the water heater is not in operation, there will be a flow of air by convection through the flues, with the resulting transfer of heat from the heated water in the tank to the air passing upwardly through the flues. This can result in considerable heat loss during standby periods.
The typical gas-fired water heater also normally includes a draft hood, which acts to prevent blow-out of the pilot light due to downdrafts. The use of a draft hood can also result in considerable heat loss from the building, because heated air from the building can continually flow by convection through the draft hood and the flue to the exterior.
In an attempt to increase the efficiency of the water heater, submersible chamber water heaters have been developed. With heaters of this type, the burner, instead of being mounted below the lower head, is positioned in a closed combustion chamber located within the lower portion of the tank. Waste gases are forced through or withdrawn from the combustion chamber by a blower and can be directly discharged to the atmosphere.
U.S. Pat. No. 4,651,714 describes a submersible chamber water heater, including a tubular member that is mounted in an opening in the side of the tank and extends horizontally across the lower portion of the tank, defining a combustion chamber. An elongated burner is positioned within the combustion chamber and the waste gases of combustion generated by igniting a fuel-air mixture are discharged from the inner end of the tubular member and are directed into a series of heat exchange tubes, which are positioned beneath the combustion chamber. The outer ends of the heat exchanger tubes extend through the wall of the tank and communicate with a collector which is connected to a flue. The water heater, as described in U.S. Pat. No. 4,651,714 provides improved efficiency for the water heating operation and minimizes stacking or stratification of the water within the tank.